If you put it in an outgoing message, you'll have to either delete that
message
or move it to the Drafts folder. Sometimes this requires that you
disconnect
from the internet while doing this. If it refuses to do either, download
and
install this hotfix, with Windows Mail not running:
http://support.microsoft.com/default.aspx/kb/941090
Although it's labelled as for messages stuck in the Outbox, it also works in
other folders. If you don't know whether you have a 32-bit version of
Vista or a 64-bit version, try the hotfix for the 32-bit version first.
Some
common antivirus programs, such as most of those from Norton or McAfee,
tend to cause stuck messages and other problems in Windows Mail, although
seldom immediately, so if you have such a program, remember where to find
the hotfix and hope it will install again if you need it again. A recent
version
of the Trend antivirus program also causes assorted problems in Windows
Mail.
The Vista SP1 update includes this hotfix and more, but takes longer to
install.